A bubble is an economic cycle that is characterized by the rapid escalation of market value, particularly in the price of assets. This fast inflation is followed by a quick decrease in value, or a contraction, that is sometimes referred to as a "crash" or a "bubble burst." Typically, a bubble is created by a surge in asset prices that is driven by exuberant market behavior. During a bubble, assets typically trade at a price, or within a price range, that greatly exceeds the asset's intrinsic value (the price does not align with the fundamentals of the asset).
An asset going through bubble phases doesn’t make it fraudulent. Bubbles can occur in all assets, including fiat currencies, commodities, real estate and equities.
Bitcoin has experienced four major cycles of massive 1000%+ appreciation, followed by deep drawdowns of more than 80%. Each cycle has started from a much higher price than the previous one. This is not a characteristic of one-time manias. Bitcoin's price, as well as fundamental adoption numbers, are increasing dramatically over multi-year timeframes.
It is a common refrain from people ignorant of both bitcoin, as well the dutch tulip bubble, to refer to bitcoin as "tulips". The tulip bubble was a one-time event, lasting a couple months at manic prices, and affecting relatively few people. Bitcoin, by sharp contrast, is exhibiting growth characteristics - both in price and adoption metrics - similar to an increasingly dominant tech company or protocol.